Generally, the regeneration ability of adult's nervous systems is limited. As a result, different extents of losses in sensory or movement functions and neuropathic pains will be caused once people suffer nerve injuries.
Nerve transplantation is a “Golden Rule” for treating nerve injuries at current. However, due to shortage of donors and certain risks in surgeries, it is very difficult to popularize this treatment approach. More importantly, its treatment effect is not very satisfactory.
It is highly concerned in recent years to promote repair of damaged nerves by using tissue engineering technology, especially by using artificial nerve tissue engineering scaffolds, and a series of eye-striking achievements are obtained.
However, current researches mainly focus on the aspect of low-difficulty peripheral nerve repair. There are few researches on the aspect of high-difficulty central nerve repair. This is because the regeneration ability of the central nervous system is obviously weaker than the regeneration ability of the peripheral nervous system (J. W. Fawcett, R. A. Asher, The glial scar and central nervous system repair, Brain Res. Bull. 49 (1999) 377-391). At the same time, after central nerve fibers are damaged, it is considered that they cannot be regenerated at present (Sabrina Morelli, Antonella Piscioneri, Neuronal growth and differentiation on biodegradable membranes, J Tissue Eng Regen Med (2012)). Therefore, methods applicable to repairing the peripheral nervous system at present are almost not applicable to repairing the central nervous system. As a result, no major breakthrough has been made in many years in researches on repairing damaged central nerves by using the existing tissue engineering technology. However, by comparison, remarkable effects have already been achieved in the aspect of repairing the peripheral nervous system by using tissue engineering scaffolds.
In researches on repairing the peripheral nervous system by using artificial nervous tissue engineering scaffolds, people find that the repair possibility of nerves depends on factors such as scaffold structure and chemical or biological induced stimulation, scaffolds such as hollow tubes and electrospun fiber membranes are prepared under this finding by using degradable natural macromolecular materials (such as collagen, chitosan and alginate) and synthetic degradable materials (such as polylactic acid-polyglycollic acid copolymer, polycaprolactone and polypyrrole), and certain peripheral nerve repair effects are achieved. On this basis, by inoculating some functional cells (such as Schwann cells, olfactory ensheathing cells and neural stem cells) or growth factors (such as nerve growth factors, brain-derived neurotrophic factors and glia-derived neurotrophic factors), better peripheral nerve repair effects are realized.
However, in regard to the repair of the central nervous system, no applicable artificial nerve tissue engineering scaffolds with remarkable effects have been found. As reported at present, researchers generally use gel only for a scaffold for repairing the central nervous system, and a certain effect can be achieved only under the joint effect of the inoculated cells and carried factors. It is worthy of being pointed out that the holding time of the gel scaffold in vivo is very short and a long-time repair effect cannot be provided. More importantly, as known up to now, any current research achievements cannot enable the original nerve function of tested animals to be restored. In other words, the current research achievements mainly stay at a level of in-vitro experiments, and it is still a major challenge in researches in this field to find a central nervous system repairing scaffold which has an actual application value.
In order to overcome the disadvantage that the holding time of gel is short, researchers try to use polyhydroxyalkanoate (PHA) three-dimensional nano-fibers as a scaffold for repairing the central nervous system, and the obtained achievement solves the problem that the holding time of the scaffold is short to a certain extent. However, the repair effect thereof depends on the inoculated neural stem cells (NSCs). More importantly, it still stays at a level of in-vitro experiments and no obvious practical prospect is shown.
For the medical field, when the practical prospect of a certain technology is judged, it is a fundamental indicator whether the in-vivo experiment result is effective and the repeatability is good. For cell-containing scaffolds, since the exertion of the function of cells is greatly influenced by the environment, in the process that the scaffold is implanted and the effect is shown after the scaffold is implanted, the implantation operation steps, the surrounding environment of implantation parts and the physiological environment therein will all influence the superiority of the repair effect. Therefore, the existing central nervous system repair methods not only do not show any expectable excellent animal experiment results, but also are very difficult to implement.
To sum up, it is urgent to find a tissue engineering scaffold for repairing the central nervous system, which can repair damaged central nerves, has good animal experiment effects and has a low difficulty in implementation.